1. Field of the Invention
This invention relates to a process for selective formation of a deposited film, particularly to a selective formation process for forming a deposited film of a III-V group compound in a self-alignment fashion.
The selective formation process of a deposited film according to the present invention is applicable for example, to preparation of thin films to be used for semiconductor integrated circuits, optical integrated circuits, etc.
2. Related Background Art
FIGS. 1A-1E illustrate the steps of the process for forming a thin film by photolithography of the prior art.
First, a substrate 1 comprising a material species with uniform composition as shown in FIG. 1A is washed, and then a thin film 2 is deposited on the whole surface of the substrate 1 according to various thin film depositing methods (vacuum vapor deposition method, sputtering method, plasma discharging method, MBE method, CVD method, etc.) (FIG. 1B).
Subsequently, onto the thin film 2 there is applied a photoresist 3 (FIG. 1C), and the photoresist 3 is exposed to light by use of a photomask of a desired pattern and the photoresist 3 is removed partially by development (FIG. 1D).
With the remaining photoresist 3 as the mask, the thin film 2 is etched to form a thin film 2 with a desired pattern (FIG. 1E).
By repeating such photolithographic steps, thin films of desired patterns are laminated to constitute an integrated circuit. In that case, alignment between the thin films of the respective layers becomes an extremely important factor for the characteristics of the device. Particularly, in the case of ultra-LSI where precision at the submicron level is is demanded, precision of the shape of thin films of the respective layers is also extremely important along with their alignment.
However, in the above process for forming a thin film of the prior art, it is difficult to effect necessary alignment of the photomasks with good precision, and also the precision of shape is insufficient, because thin films of desired patterns are formed by etching.
FIGS. 2A-2D illustrate the steps of the process for forming a thin film by use of lift-off method of the prior art.
First, a photoresist 4 is applied on a substrate 1 (FIG. 2A), and the photoresist 4 with a desired pattern is removed by photolithography (FIG. 2B).
Subsequently, a thin film 5 is deposited according to a thin film deposition method (FIG. 2C), and the remaining photoresist 4 is dissolved away. By this operation, the thin film on the remaining photoresist 4 is removed at the same time, whereby a thin film 5 with a desired pattern is formed. By repeating the above steps, an integrated circuit is constituted.
However, in such a thin film forming process, because a thin film is formed on a photoresist, it is required that the deposition of a thin film be performed at a temperature not higher than the resistant temperature of the photoresist, therefore, the deposition method is greatly restricted. Also, in removing the photoresist, the shape of the remaining thin film is influenced thereby and therefore precision of the shape becomes insufficient. Also, there is also the problem that it is highly probable that the side wall or the inner portion of the think film may be contaminated with carbon, a component of the photoresist.
Also, selective deposition methods, are known in which a monocrystal substrate is covered partially with an amorphous thin film, and the same material as the substrate material is epitaxially grown selectively only at the exposed portion of the monocrystal substrate. For example, there is the selective epitaxial Growth (SEG) method in which a silicon monocrystal substrate is partially covered with silicon oxide to effect selective Growth of silicon (B. D. Joyce & J. A. Baldrey, Nature vol. 195,485, 1962), and the method in which a GaAs substrate is covered partially with an amorphous thin film such as SiO.sub.2, Si.sub.3 N.sub.4, etc. to effect selectively epitaxial Growth of GaAs (P. Rai-Choudhury & D. K. Schroder, J. Electrochem. Soc., 118, 107, 1971), etc.
However, because these selective deposition methods rely on growing selectively the monocrystal semiconductor of the same kind from the exposed surface of a monocrystal substrate, they are limited in that the deposition surface for the base must also be monocrystalline, and therefore not applicable to polycrystalline substrates, amorphous insulating substrates.
Thus, the deposited film forming methods of the prior art are limited in the number of available substrates, and further, problems in shape of the pattern, and dimensional precision of the deposited film once formed.